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  • Writing a DBMS in Python

    - by Matt Luongo
    Hey guys, I'm working on a basic DBMS as a pet project and planning to prototype in Python. I figure there's a reason there are only a few Python databases, and my gut agrees that my favorite language will be too slow to act as an honest performing database, but I'm looking forward to using it to learn what I need quickly. Would someone please contradict me? Is Python as ill-suited right now for this sort of thing as I think?

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  • How to efficiently show many Images? (iPhone programming)

    - by Thomas
    In my application I needed something like a particle system so I did the following: While the application initializes I load a UIImage laserImage = [UIImage imageNamed:@"laser.png"]; UIImage *laserImage is declared in the Interface of my Controller. Now every time I need a new particle this code makes one: // add new Laserimage UIImageView *newLaser = [[UIImageView alloc] initWithImage:laserImage]; [newLaser setTag:[model.lasers count]-9]; [newLaser setBounds:CGRectMake(0, 0, 17, 1)]; [newLaser setOpaque:YES]; [self.view addSubview:newLaser]; [newLaser release]; Please notice that the images are only 17px * 1px small and model.lasers is a internal array to do all the calculating seperated from graphical output. So in my main drawing loop I set all the UIImageView's positions to the calculated positions in my model.lasers array: for (int i = 0; i < [model.lasers count]; i++) { [[self.view viewWithTag:i+10] setCenter:[[model.lasers objectAtIndex:i] pos]]; } I incremented the tags by 10 because the default is 0 and I don't want to move all the views with the default tag. So the animation looks fine with about 10 - 20 images but really gets slow when working with about 60 images. So my question is: Is there any way to optimize this without starting over in OpenGl ES? Thank you very much and sorry for my english! Greetings from Germany, Thomas

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  • Explanation for expires header

    - by sushil bharwani
    I have a joomla application working on Apache.To improve site performace we have written a .htaccess file to root of the application with setting a far future expires header to all the static content. As desired first time the files load in fresh with 200 status code. when again click on the same link many of the files are served directly from cache. I need explanation for two things When i press f5 then a number of files load with 304 status code however i expected them to be coming directly from cache without hitting the server for a status header? When i close the browser and come back to the same page again i see the same thing happening a number of files load with 304 status code although i thought they will load directly from the browser cache? I understand that 304 also servs file from browser cache but i want to avoid the header communication between servers as my static files wont ever change. Also i want to add that my requests are over a https connection does that create any issue.

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  • Combine static files or load in parallel

    - by Niall Collins
    I am at present introducing code to my site to combine css and javascript files. Is there a way without having to include an external library to load javascript asynchronously or in parallel? I have read on some blogs that combining of files can be counter productive as the load of the http request can be large and its better to load multiple files in parallel. Opinions on this? I am caching my javascript/css. And would have thought it was better to combine rather than have multiple http requests.

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  • XDocument holding onto Memory?

    - by Jon
    I have an appplication that does a XDocument.Load from a 20mb file and then gets passed to a form to view its contents: openFileDialog1.FileName = ""; if (openFileDialog1.ShowDialog() == DialogResult.OK) { AuditFile = XDocument.Load(openFileDialog1.FileName); fmAuditLogViewer AuditViewer = new fmAuditLogViewer(); AuditViewer.ReportDocument = AuditFile; AuditViewer.Init(); AuditViewer.ShowDialog(); AuditViewer.Dispose(); AuditFile.RemoveNodes(); AuditFile = null; } In Task Manager I can see the memory being used by my application shoot up when I open this file. When I have finished viewing this file in my application I call : myXDocument.RemoveNodes(); myXDocument = null; However the memory use in Task Manager is still pretty high against my app. Is the XDocument still being held in memory and can I decrease the memory usage by my app?

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  • Slow retrieval of data in SQLITE takes a long using ContentProvider

    - by Arlyn
    I have an application in Android (running 4.0.3) that stores a lot of data in Table A. Table A resides in SQLite Database. I am using a ContentProvider as an abstraction layer above the database. Lots of data here means almost 80,000 records per month. Table A is structured like this: String SQL_CREATE_TABLE = "CREATE TABLE IF NOT EXISTS " + TABLE_A + " ( " + COLUMN_ID + " INTEGER PRIMARY KEY NOT NULL" + "," + COLUMN_GROUPNO + " INTEGER NOT NULL DEFAULT(0)" + "," + COLUMN_TIMESTAMP + " DATETIME UNIQUE NOT NULL" + "," + COLUMN_TAG + " TEXT" + "," + COLUMN_VALUE + " REAL NOT NULL" + "," + COLUMN_DEVICEID + " TEXT NOT NULL" + "," + COLUMN_NEW + " NUMERIC NOT NULL DEFAULT(1)" + " )"; Here is the index statement: String SQL_CREATE_INDEX_TIMESTAMP = "CREATE INDEX IF NOT EXISTS " + TABLE_A + "_" + COLUMN_TIMESTAMP + " ON " + TABLE_A + " (" + COLUMN_TIMESTAMP + ") "; I have defined the columns as well as the table name as String Constants. I am already experiencing significant slow down when retrieving this data from Table A. The problem is that when I retrieve data from this table, I first put it in an ArrayList and then I display it. Obviously, this is possibly the wrong way of doing things. I am trying to find a better way to approach this problem using a ContentProvider. But this is not the problem that bothers me. The problem is for some reason, it takes a lot longer to retrieve data from other tables which have only upto 12 records maximum. I see this delay increase as the number of records in Table A increase. This does not make any sense. I can understand the delay if I retrieve data from Table A, but why the delay in retrieving data from other tables. To clarify, I do not experience this delay if Table A is empty or has less than 3000 records. What could be the problem?

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  • data sync from rails with iphone sqlite db

    - by Markus
    Hi all, I'm wondering whether there is a bossibility to export some selected data from my rails mysql db to a other sqlite db. The aim is to send that sqlite file directly to my iPhone application... That way I don't have to do a lot of xml integration in the iPhone app. That seems to be very slow... Markus

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  • How to speed up the reading of innerHTML in IE8?

    - by Dennis Cheung
    I am using JQuery with the DataTable plugin, and now I have a big performnce issue on the following line. aLocalData[jInner] = nTds[j].innerHTML; // jquery.dataTables.js:2220 I have a ajax call, and result string in HTML format. I convert them into HTML nodes, and that part is ok. var $result = $('<div/>').html(result).find("*:first"); // simlar to $result=$(result) but much more faster in Fx Then I activate enable the result from a plain table to a sortable datatable. The speed is acceptable in Fx (around 4sec for 900 rows), but unacceptable in IE8 (more then 100 seconds). I check it deep using the buildin profiler, and found the above single line take all 99.9% of the time, how can I speed it up? anything I missed? nTrs = oSettings.nTable.getElementsByTagName('tbody')[0].childNodes; for ( i=0, iLen=nTrs.length ; i<iLen ; i++ ) { if ( nTrs[i].nodeName == "TR" ) { iThisIndex = oSettings.aoData.length; oSettings.aoData.push( { "nTr": nTrs[i], "_iId": oSettings.iNextId++, "_aData": [], "_anHidden": [], "_sRowStripe": '' } ); oSettings.aiDisplayMaster.push( iThisIndex ); aLocalData = oSettings.aoData[iThisIndex]._aData; nTds = nTrs[i].childNodes; jInner = 0; for ( j=0, jLen=nTds.length ; j<jLen ; j++ ) { if ( nTds[j].nodeName == "TD" ) { aLocalData[jInner] = nTds[j].innerHTML; // jquery.dataTables.js:2220 jInner++; } } } }

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  • KD-Trees and missing values (vector comparison)

    - by labratmatt
    I have a system that stores vectors and allows a user to find the n most similar vectors to the user's query vector. That is, a user submits a vector (I call it a query vector) and my system spits out "here are the n most similar vectors." I generate the similar vectors using a KD-Tree and everything works well, but I want to do more. I want to present a list of the n most similar vectors even if the user doesn't submit a complete vector (a vector with missing values). That is, if a user submits a vector with three dimensions, I still want to find the n nearest vectors (stored vectors are of 11 dimensions) I have stored. I have a couple of obvious solutions, but I'm not sure either one seem very good: Create multiple KD-Trees each built using the most popular subset of dimensions a user will search for. That is, if a user submits a query vector of thee dimensions, x, y, z, I match that query to my already built KD-Tree which only contains vectors of three dimensions, x, y, z. Ignore KD-Trees when a user submits a query vector with missing values and compare the query vector to the vectors (stored in a table in a DB) one by one using something like a dot product. This has to be a common problem, any suggestions? Thanks for the help.

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  • Are Hibernate named HQL queries (in annotations) optimised?

    - by Graham Lea
    A new colleague has just suggested using named HQL queries in Hibernate with annotations (i.e. @NamedQuery) instead of embedding HQL in our XxxxRepository classes. What I'd like to know is whether using the annotation provides any advantage except for centralising quueries? In particular, is there some performances gain, for instance because the query is only parsed once when the class is loaded rather than every time the Repository method is executed?

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  • Server Benchmarking: What tools to use with my real-world test data

    - by mdemmitt
    I want to benchmark a new server using historical HTTP-request data. I have a textfile that contains one day's worth of real historical requests to a production server. What is the best tool for sending that list of requests on the server I'm testing? The tool I use should be able to configure the following: Number of threads making the requests Number of requests/second sent A list of request URLs to use when making the requests. Apache Bench seems like a close fit. However, Bench does not seem to be able to take in a list of request URLs as a parameter. What would you recommend?

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  • Best way to split a string by word (SQL Batch separator)

    - by Paul Kohler
    I have a class I use to "split" a string of SQL commands by a batch separator - e.g. "GO" - into a list of SQL commands that are run in turn etc. ... private static IEnumerable<string> SplitByBatchIndecator(string script, string batchIndicator) { string pattern = string.Concat("^\\s*", batchIndicator, "\\s*$"); RegexOptions options = RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.Multiline; foreach (string batch in Regex.Split(script, pattern, options)) { yield return batch.Trim(); } } My current implementation uses a Regex with yield but I am not sure if it's the "best" way. It should be quick It should handle large strings (I have some scripts that are 10mb in size for example) The hardest part (that the above code currently does not do) is to take quoted text into account Currently the following SQL will incorrectly get split: var batch = QueryBatch.Parse(@"-- issue... insert into table (name, desc) values('foo', 'if the go is on a line by itself we have a problem...')"); Assert.That(batch.Queries.Count, Is.EqualTo(1), "This fails for now..."); I have thought about a token based parser that tracks the state of the open closed quotes but am not sure if Regex will do it. Any ideas!?

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  • Fast Lightweight Image Comparisson Metric Algorithm

    - by gav
    Hi All, I am developing an application for the Android platform which contains 1000+ image filters that have been 'evolved'. When a user selects a photo I want to present the most relevant filters first. This 'relevance' should be dependent on previous use cases. I have already developed tools that register when a filtered image is saved; this combination of filter and image can be seen as the training data for my system. The issue is that the comparison must occur between selecting an image and the next screen coming up. From a UI point of view I need the whole process to take less that 4 seconds; select an image- obtain a metric to use for similarity - check against use cases - return 6 closest matches. I figure with 4 seconds I can use animations and progress dialogs to keep the user happy. Due to platform contraints I am fairly limited in the computational expense of the algorithm. I have implemented a technique adapted from various online tutorials for running C code on the G1 and hence this language is available Specific Constraints; Qualcomm® MSM7201A™, 528 MHz Processor 320 x 480 Pixel bitmap in 32 bit ARGB ~ 2 seconds computational time for the native method to get the metric ~ 2 seconds to compare the metric of the current image with training data This is an academic project so all ideas are welcome, anything you can think of or have heard about would be of interest to me. My ideas; I want to keep the complexity down (O(n*m)?) by using pixel data only rather than a neighbourhood function I was looking at using the Colour historgram/Greyscale histogram/Texture/Entropy of the image, combining them to make the measure. There will be an obvious loss of information but I need the resultant metric to be substantially smaller than the memory footprint of the image (~0.512 MB) As I said, any ideas to direct my research would be fantastic. Kind regards, Gavin

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  • Problem measuring N times the execution time of a code block

    - by Nazgulled
    EDIT: I just found my problem after writing this long post explaining every little detail... If someone can give me a good answer on what I'm doing wrong and how can I get the execution time in seconds (using a float with 5 decimal places or so), I'll mark that as accepted. Hint: The problem was on how I interpreted the clock_getttime() man page. Hi, Let's say I have a function named myOperation that I need to measure the execution time of. To measure it, I'm using clock_gettime() as it was recommend here in one of the comments. My teacher recommends us to measure it N times so we can get an average, standard deviation and median for the final report. He also recommends us to execute myOperation M times instead of just one. If myOperation is a very fast operation, measuring it M times allow us to get a sense of the "real time" it takes; cause the clock being used might not have the required precision to measure such operation. So, execution myOperation only one time or M times really depends if the operation itself takes long enough for the clock precision we are using. I'm having trouble dealing with that M times execution. Increasing M decreases (a lot) the final average value. Which doesn't make sense to me. It's like this, on average you take 3 to 5 seconds to travel from point A to B. But then you go from A to B and back to A 5 times (which makes it 10 times, cause A to B is the same as B to A) and you measure that. Than you divide by 10, the average you get is supposed to be the same average you take traveling from point A to B, which is 3 to 5 seconds. This is what I want my code to do, but it's not working. If I keep increasing the number of times I go from A to B and back A, the average will be lower and lower each time, it makes no sense to me. Enough theory, here's my code: #include <stdio.h> #include <time.h> #define MEASUREMENTS 1 #define OPERATIONS 1 typedef struct timespec TimeClock; TimeClock diffTimeClock(TimeClock start, TimeClock end) { TimeClock aux; if((end.tv_nsec - start.tv_nsec) < 0) { aux.tv_sec = end.tv_sec - start.tv_sec - 1; aux.tv_nsec = 1E9 + end.tv_nsec - start.tv_nsec; } else { aux.tv_sec = end.tv_sec - start.tv_sec; aux.tv_nsec = end.tv_nsec - start.tv_nsec; } return aux; } int main(void) { TimeClock sTime, eTime, dTime; int i, j; for(i = 0; i < MEASUREMENTS; i++) { printf(" » MEASURE %02d\n", i+1); clock_gettime(CLOCK_REALTIME, &sTime); for(j = 0; j < OPERATIONS; j++) { myOperation(); } clock_gettime(CLOCK_REALTIME, &eTime); dTime = diffTimeClock(sTime, eTime); printf(" - NSEC (TOTAL): %ld\n", dTime.tv_nsec); printf(" - NSEC (OP): %ld\n\n", dTime.tv_nsec / OPERATIONS); } return 0; } Notes: The above diffTimeClock function is from this blog post. I replaced my real operation with myOperation() because it doesn't make any sense to post my real functions as I would have to post long blocks of code, you can easily code a myOperation() with whatever you like to compile the code if you wish. As you can see, OPERATIONS = 1 and the results are: » MEASURE 01 - NSEC (TOTAL): 27456580 - NSEC (OP): 27456580 For OPERATIONS = 100 the results are: » MEASURE 01 - NSEC (TOTAL): 218929736 - NSEC (OP): 2189297 For OPERATIONS = 1000 the results are: » MEASURE 01 - NSEC (TOTAL): 862834890 - NSEC (OP): 862834 For OPERATIONS = 10000 the results are: » MEASURE 01 - NSEC (TOTAL): 574133641 - NSEC (OP): 57413 Now, I'm not a math wiz, far from it actually, but this doesn't make any sense to me whatsoever. I've already talked about this with a friend that's on this project with me and he also can't understand the differences. I don't understand why the value is getting lower and lower when I increase OPERATIONS. The operation itself should take the same time (on average of course, not the exact same time), no matter how many times I execute it. You could tell me that that actually depends on the operation itself, the data being read and that some data could already be in the cache and bla bla, but I don't think that's the problem. In my case, myOperation is reading 5000 lines of text from an CSV file, separating the values by ; and inserting those values into a data structure. For each iteration, I'm destroying the data structure and initializing it again. Now that I think of it, I also that think that there's a problem measuring time with clock_gettime(), maybe I'm not using it right. I mean, look at the last example, where OPERATIONS = 10000. The total time it took was 574133641ns, which would be roughly 0,5s; that's impossible, it took a couple of minutes as I couldn't stand looking at the screen waiting and went to eat something.

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  • Non-latin-characters ordering in database with "order by"

    - by nybon
    I just found some strange behavior of database's "order by" clause. In string comparison, I expected some characters such as '[' and '_' are greater than latin characters such as 'i' considering their orders in the ASCII table. However, the sorting results from database's "order by" clause is different with my expectation. Here's my test: SQLite version 3.6.23 Enter ".help" for instructions Enter SQL statements terminated with a ";" sqlite> create table products(name varchar(10)); sqlite> insert into products values('ipod'); sqlite> insert into products values('iphone'); sqlite> insert into products values('[apple]'); sqlite> insert into products values('_ipad'); sqlite> select * from products order by name asc; [apple] _ipad iphone ipod This behavior is different from Java's string comparison (which cost me some time to find this issue). I can verify this in both SQLite 3.6.23 and Microsoft SQL Server 2005. I did some web search but cannot find any related documentation. Could someone shed me some light on it? Is it a SQL standard? Where can I find some information about this? Thanks in advance.

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  • What's the difference between reflow and repaint?

    - by Jon Raasch
    I'm a little unclear on the difference between reflow + repaint (if there's any difference at all) Seems like reflow might be shifting the position of various DOM elements, where repaint is just rendering a new object. E.g. reflow would occur when removing an element and repaint would occur when changing its color. Is this true?

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  • Update mapping table in Linq

    - by Gary McGill
    I have a table Customers with a CustomerId field, and a table of Publications with a PublicationId field. Finally, I have a mapping table CustomersPublications that records which publications a customer can access - it has two fields: CustomerId field PublicationId. For a given customer, I want to update the CustomersPublications table based on a list of publication ids. I want to remove records in CustomersPublications where the PublicationId is not in the list, and add new records where the PublicationId is in the list but not already in the table. This would be easy in SQL, but I can't figure out how to do it in Linq. For the delete part, I tried: var recordsToDelete = dataContext.CustomersPublications.Where ( cp => (cp.CustomerId == customerId) && ! publicationIds.Contains(cp.PublicationId) ); dataContext.CustomersPublications.DeleteAllOnSubmit(recordsToDelete); ... but that didn't work. I got an error: System.NotSupportedException: Method 'Boolean Contains(Int32)' has no supported translation to SQL So, I tried using Any(), as follows: var recordsToDelete = dataContext.CustomersPublications.Where ( cp => (cp.CustomerId == customerId) && ! publicationIds.Any(p => p == cp.PublicationId) ); ... and this just gives me another error: System.NotSupportedException: Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator Any pointers? [I have to say, I find Linq baffling (and frustrating) for all but the simplest queries. Better error messages would help!]

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  • How can I get page faults statistics from kernel

    - by osgx
    Hello How can I get page faults statistics from kernel for my application while it is running? What about other events, like inter-cpu migrations count in SMP nodes, or number of context switches? I want to count such events for various small parts of the program. Thanks.

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  • Using TCP Acks to measure latency to a server?

    - by Ted Graham
    I am trying to measure latency to a server that I don't control. This is in a colocated environment, so the latency is on the order of 500 us (.5 ms). I understand that Cisco gear frequently deprioritizes ICMP traffic, making ping times unreliable. Is there a way for me to tell if this is the case on the gear I am traversing? Can I use TCP acknowledgements to determine the minimum latency to the remote server? To do this, I would somehow need to force the remote server to send a TCP ack immediately on receiving my data.

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  • devArt's dotConnect for Oracle vs. ODP.net/OCI performanc.

    - by Sieg
    Does anybody have any experience going from ODP.net to devArt's dotConnect for Oracle? Some initial testing is showing Direct Connect in 64bit dotConnect running 30% slower at times than our original ODP.net/OCI 32 bit solution. Trying to determine if that's normal or if something may be wrong in my testing approach. Thanks!

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  • Strategy Pattern with Type Reflection affecting Performances ?

    - by Aurélien Ribon
    Hello ! I am building graphs. A graph consists of nodes linked each other with links (indeed my dear). In order to assign a given behavior to each node, I implemented the strategy pattern. class Node { public BaseNodeBehavior Behavior {get; set;} } As a result, in many parts of the application, I am extensively using type reflection to know which behavior a node is. if (node.Behavior is NodeDataOutputBehavior) workOnOutputNode(node) .... My graph can get thousands of nodes. Is type reflection greatly affecting performances ? Should I use something else than the strategy pattern ? I'm using strategy because I need behavior inheritance. For example, basically, a behavior can be Data or Operator, a Data behavior can IO, Const or Intermediate and finally an IO behavior can be Input or Output. So if I use an enumeration, I wont be able to test for a node behavior to be of data kind, I will need to test it to be [Input, Output, Const or Intermediate]. And if later I want to add another behavior of Data kind, I'm screwed, every data-testing method will need to be changed.

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  • Good .NET library for fast streaming / batching trigonometry (Atan)?

    - by Sean
    I need to call Atan on millions of values per second. Is there a good library to perform this operation in batch very fast. For example, a library that streams the low level logic using something like SSE? I know that there is support for this in OpenCL, but I would prefer to do this operation on the CPU. The target machine might not support OpenCL. I also looked into using OpenCV, but it's accuracy for Atan angles is only ~0.3 degrees. I need accurate results.

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  • Optimizing MySQL for ALTER TABLE of InnoDB

    - by schuilr
    Sometime soon we will need to make schema changes to our production database. We need to minimize downtime for this effort, however, the ALTER TABLE statements are going to run for quite a while. Our largest tables have 150 million records, largest table file is 50G. All tables are InnoDB, and it was set up as one big data file (instead of a file-per-table). We're running MySQL 5.0.46 on an 8 core machine, 16G memory and a RAID10 config. I have some experience with MySQL tuning, but this usually focusses on reads or writes from multiple clients. There is lots of info to be found on the Internet on this subject, however, there seems to be very little information available on best practices for (temporarily) tuning your MySQL server to speed up ALTER TABLE on InnoDB tables, or for INSERT INTO .. SELECT FROM (we will probably use this instead of ALTER TABLE to have some more opportunities to speed things up a bit). The schema changes we are planning to do is adding a integer column to all tables and make it the primary key, instead of the current primary key. We need to keep the 'old' column as well so overwriting the existing values is not an option. What would be the ideal settings to get this task done as quick as possible?

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